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Looking to convert from oil heating and water heating to a solar PV system

CG Vermonter | Posted in Mechanicals on

I know it won’t be cheap, but I want to shift my energy use from oil to Solar PV.

Currently I have a hot water system and baseboard hot water heating.
I plan on installing a Solar array and so I would like to convert to an all electric design.

Do I take everything out and install electric baseboard heaters and an electric Hot water heater?

Or would it make more sense to use my current system and just find a way to heat the water with the PV array instead of with oil?

Ideas?

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Replies

  1. TJ Elder | | #1

    Chris, what is your location? You'll have to be somewhere very clear and sunny to make a solar thermal system work for space heating. Using PV to heat water is not efficient, but solar hot water can work, it's just hard to get enough heat that way for space heating.

  2. CG Vermonter | | #2

    Thanks Thomas. My location is in VT.
    But let me be clear. I understand that I will not be implementing the most efficient system by using PV. However, we have a decent net metering system here so as long as I put in a properly sized solar array, I can use the PV to heat my water year round.
    My primary goal is to shift from oil dependency to producing my own electricity to run my systems on.
    But from your response I am thinking it would make the most sense to remove my current heating system and replace it with baseboard electric. And also install an electric water heater.

  3. TJ Elder | | #3

    Chris,

    I should have added that if you were somewhere sunny enough for solar hot water to provide space heating, you wouldn't need it anyway because passive solar would keep you toasty. In VT it's not so sunny in the winter. Net metering will work if the goal is net zero (annually) rather than depending on the PV to provide all the power you need during the winter.

    Something to consider about electric heating is COP, the coefficient of performance. The benchmark is electric resistance (what you've proposed) with a COP of 1. It's possible to get 2-4x as much heat from the same power using heat pumps. A mini-split system could provide space heat, and there are also heat pump water heaters, but they're not well suited to a cold climate.

  4. Philipp Gross | | #4

    Chris, I know you are very specific with your question and goals but as often suggested on this site it makes more sense to upgrade insulation and airtightness (building envelope) first and then add renewables. We did a recent case study comparing a 1700 SF building build to Minnesota code (where I life and work) and build to the Passive House standard. For the code building a 25kWp PV array is necessary to achieve net zero.That is if the building uses natural gas for heating (even worse for electric resistance). A PV array that size does not fit on the roof. For the Passive House the array shrinks to 4.5 kWp. To my point: You should first spent a small amount of the money on a professional that knows about stuff like that, then improve your building envelope and then (if there is any money left) add renewables. At least that is the way to go if you do this for the environments sake and want to degrease your carbon footprint.

  5. GBA Editor
    Martin Holladay | | #5

    CG,
    Philipp gave you good advice. Installing a PV system is rarely the first step if you are interested in reducing your carbon footprint or lowering your energy bills. Reduce air leaks in your home and improve your insulation levels; be sure your lights are all CFLs.

    If you ever decide to heat your home with electricity, get one or two ductless minisplit air-source heat pumps. Don't use electric resistance heat.

  6. CG Vermonter | | #6

    Thanks for the responses.
    However, my question was very specific for a reason. I was looking for some technical help on a solution to a problem. I don't want to get into all of the details here, but it generally has to do with massive flooding, and waste issues concerning giant tanks of oil in the basement.
    So as much as I appreciate the help on how to reduce my carbon footprint, my primary goal here is as I stated at the beginning. It is about shifting my consumption from one source of fuel to another.

    Also, a well built home in Vermont is typically a very efficient home by definition. Our builders up here have been making homes comfortable in the winter for a very long time. My return on increased insulation and reducing air leaks will be very minimal. Also it will not address the fact that I am looking for a way to stop using oil as my fuel source.
    Furthermore I am holding out on filling my house with mercury laden CFLs until the LED bulbs hit the market. (there are already a few but not very powerful yet)

    And lastly, I must admit I am a bit of sceptic when it comes to the ductless minisplits in a climate such as ours. Too many of the professionals I talk to are not convinced they are ready to be used reliably.

  7. GBA Editor
    Martin Holladay | | #7

    CG,
    It sounds like you have strong opinions, and you know exactly what you want. So go ahead with your plan -- any advice from this forum doesn't appear to be necessary or useful to you.

  8. Thaddeus Cox | | #8

    Speaking from a strictly laws-of-physics point of view, using PVs for heat is the least efficient option. PV in the best possible case is only about 30% efficient. Since you already have a hot water system, it would be much more efficient to use solar collectors to heat the water directly, not to mention much cheaper to setup.

    Regardless, in Vermont you're going to be C O L D unless you have backup heat.

    FWIW, HVAC professionals who are skeptical about "new" technology are coming from a position of fear-of-the-unknown. For one thing minsplits are NOT new - they are extremely common in every other part of the world. The heat pumps that are common in the US are stone-age compared to the variable-flow/inverter based HPs that are just coming out here but have been used for years overseas.

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